A method for performing a fine patterning on a workpiece is generally known as a fine patterning technique, in which a photoresist is applied on the surface of a target object to be processed (i.e., workpiece), the photoresist is then finely exposed to light using a laser exposure device, and finally etching is performed.
In order to expose a photoresist layer to light, for example, Japanese Laid-open Patent Application, Publication No. 04-345921 discloses a method for forming recessed portions by causing the photoresist layer to absorb light, so that due to generated heat, the photoresist material is decomposed, vaporized, and scattered. As with this method, if processing is performed using the heat derived from light, only that portion which reaches a predetermined temperature or more undergoes a change of shape. Therefore, unlike a chemical change due to exposure of light, a so-called super-resolution processing method is available which can form a fine hole having a diameter smaller than the light spot. This processing is carried out using a device similar to a pickup for an optical disc, and is advantageous in terms of achieving a cheap and high-speed fine processing. A further advantage is that a development of the photoresist layer becomes unnecessary and the processing of the workpiece can be performed by a simple process.
However, if the so-called thermally deformable heat mode resist-type photoresist layer is exposed to light for processing as described above, scattered materials derived from the photoresist material often attach to an object lens of the exposure device and therefore it is necessary to frequently clean the object lens.
Further, when a fine processing is performed by condensing the light beam to a narrow beam at the time of exposure, it is a customary practice to increase the numerical aperture (NA) of the object lens. However, increasing the NA will result in decreased focal length, and hence the distance between the workpiece and the object lens becomes shorter, so that even a slight vibration will cause a collision of the object lens with the workpiece and disadvantageously damage the workpiece. This disadvantage is particularly noticeable in the case of an autofocus servo control because the object lens is moved.
In view of the above disadvantage, the present invention seeks to provide a processing method which can prevent a workpiece from being damaged and in the case of using a thermally deformable heat mode resist-type photoresist material, prevent an object lens from being soiled.